London Sewerage System - Modern Development Needs

Modern Development Needs

The original system was designed to cope with 6.5 mm (1/4”) per hour of rainfall within the catchment area, and supported a smaller population than today’s. London's growth has put pressure on the capacity of the sewerage system. During storms, for example, high levels of rainfall (in excess of 6 mm per hour) in a short period of time can overwhelm the system. Sewers and treatment works are unable to cope with the large volumes of rainwater entering the system. Rainwater mixes with sewage in combined sewers and excess mixed water is discharged into the Thames. If this does not happen quickly enough, localised flooding occurs (surcharge). Such sanitary sewer overflow can mean streets becoming flooded with a mixture of water and sewage, causing a health risk.

In redeveloping the Isle of Dogs and Royal Docks areas of east London during the late 1980s and early 1990s, the London Docklands Development Corporation invested in major new drainage infrastructure to manage future sewage and surface water run-off from proposed developments. Consulting engineer Sir William Halcrow & Partners designed a system of large diameter tunnels served by new pumping stations. In the Royal Docks, approximately 16 miles (25 km) of foul and surface water drains were built, plus pumping stations at Tidal Basin (designed by Richard Rogers Partnership) and North Woolwich (architect: Nicholas Grimshaw). The Isle of Dogs drainage network is served by a stormwater pumping station situated in Stewart Street, designed by John Outram Associates.

Increasing the carrying capacity of London’s sewerage system has been debated for some years. Proposals for the 'Thames Tideway' include a wide diameter storage-and-transfer tunnel (internal diameters of 7.2 m and 9 m have been suggested), 22 miles (35 km) long, underneath the riverbed of the Thames between Hammersmith in the west and Beckton/Crossness in the east, but as the cost of such a megaproject is likely to be substantial (estimated at £1.7 billion in 2004), investment decisions have been slow in forthcoming. In March 2007 the Mayor of London announced that the project will proceed with completion expected by 2020.

Because design and construction of such a tunnel will take an estimated 15 years, a shorter-term (and slightly lower cost) interim solution has also been developed. This £1.6 billion scheme (2006 prices) involves two shorter tunnels (one taking storm water from Hammersmith to Battersea for treatment or storage, the other carrying water from Abbey Mills south to the river at Beckton) and improvements to associated treatment facilities.